Fluid circuit



United States Patent [72] Inventor Michael J. Hoglund 3,237,859 3/1966 Hatch 235/201(P.F.)UX Blaine, Minnesota 3,338,515 8/1967 Dexter.... 235/20l(P.F.)UX [21] App]. No. 690,460 3,340,885 9/1967 Bauer l37/8l.5 [22] Filed Dec. 14, 1967 3,366,327 1/1968 Ringwall et a1. 235/200(P.F.)UX [45] Patented Sept. 29,1970 3,392,739 7/1968 Taplin et a1 |37/8] 5X [73] Assignee Honeywell inc. 3,407,828 10/1968 Jones 137/81.5 Minneapolis, Minnesota 3,413,994 12/1968 Somers 137/81.5 a corporation of Delaware 3,417,772 l2/l 968 Schaeffer 137/815 Primary Examiner-Samuel Scott 1 FLUID CIRCUIT AnorneysRoger W. Jensen, Charles J. Ungemach and 11 Claims, 2 DrawingFigs. R ld T R ili [52] U.S. Cl

[51 1 Int. Cl [50] Field of Search ABSTRACT: A fluidic circuit, the output signal of which is a I 5 6] References Cited variable function of the input signal supplied thereto. The circurt comprises means for supplying a common input signal to UNITED STATES PATENTS both a fluidic variable gain circuit and a control circuit which 5. 1 H 64 the Z35/2 |(P.F.)UX provides the variable gain circuit with gain control signals.

:21 7 'l .26 I :28 4 I l 51 r I a i 4 I D5 h as 5 J i l I l fig 81/ a2 g lsif 7| 1 l i 8/ mi i a I F |o| i 40 1 i I I l l 35 Fl I l s: I I 1 i '24 I I l I a? l l I i s; i 1 24 l m I l I l 7 i I l i J 1 17 l l IO 1 1 If: "1 I I l I i 7' "6 L Q Patented Sept. 29, 1970 FIG. I

I NVENTOR. MICHAEL J. HOGLUND AP OUTPUT AP INPUT FLUID CIRCUIT BACKGROUND OF THE INVENTION The invention herein described relates generally to fluid handling apparatus, and more specifically to fluidic function generating circuits.

Fluid amplifiers and various other fluidic devices have been known in the art for some time. However, only recently has the fluidics art advanced to the point that complete systems utilizing fluidic components are feasible. The recent interest in fluidic systems design has increased the need for more flexible fluidic components and circuits. Many ofthe fluidic systems of interest require variable means for producing nonlinear and discontinuous mathematical functions. Thus, an increasing need exists for flexible fluidic function generating circuits.

One prior art solution to the problem of fluidically providing an output signal which is a prescribed function of an input signal has been to use a special fluid amplifier having a specially characterized splitter element tlherewithin. Outlet passages are provided on opposite sides of the splitter element. As a power stream is deflected generally along the length of the splitter element by appropriate input signals, the output signal, taken between opposing outlet passages, varies in accordance with the splitter element characterization.

Another prior art solution to this problem has been to combine an analog fluid amplifier with one or more flow restrictions of the orifice and/or laminar flow type in a circuit configuration which produces an output signal having the desired relationship to the input signal. The function generating properties of a device of this type are based on the facts that the weight flow versus pressure drop characteristic of an orifice restriction resembles a square root function and that the weight flow versus pressure drop characteristic of a laminar flow restriction is substantially linear. Thus, when one or more of these restrictions is provided in the control, outlet and/or feedback passages of an analog fluid amplifier, fluid signals representing a variety of mathematical functions can be produced.

In a function generator employing either of these prior art techniques, the relationship of the output signal to the input signal is based on the structural configuration of the device or circuit. Thus, the function to be generated is fixed at the time the device or circuit is fabricated and can be changed only by means of structural modifications.

In many fluidic systems employing function generators, it is necessary to tailor the generated function to obtain optimum system performance. Prior art function generators requiring structural modifications to accomplish minor changes in the generated function are highly undesirable in such systems. In addition, many fluidic systems require function generators capable of generating functions which are quickly and easily variable in response to a command or control signal. Function generators which require structural modifications to alter the generated function are not satisfactory in these applications. Thus, it is apparent that prior art function generators are not generally satisfactory for use in many fluidic systems.

SUMMARY OF THE INVENTION The applicant's fluidic function generator comprises input means which supplies common fluid input signals to a fluidic variable gain circuit and a control circuit. The control circuit provides the variable gain circuit with gain control signals having a prescribed relationship to the input signals. The gain of the variable gain circuit is controlled by the gain control signals provided thereto. Output means is provided at the outlet of the variable gain circuit. Means may be provided for supplying variable bias pressures to the input and output means. In addition, means may be included for providing variable supply and bias pressures to the control circuit and the variable gain circuit.

In accordance with the teachings of this invention the applicants unique function generator comprises only standard general purpose fluidic components. The relationship between the input signals and the output signals of the applicant's function generator can be widely varied by changing only the supply and bias pressures provided thereto. Contrary to the prior art, no structural alterations are required to change the generated function. Further, the applicants unique circuit can generate easily variable combinations of linear and nonlinear, continuous and discontinuous functions.

BRIEF DESCRIPTION OF THE DRAWING FIG. l is a schematic representation of the applicant's fluidic function generator; and

FIG. 2 is a plurality of curves illustrating some of the input signal versus'output signal relationships of the applicants function generator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral generally refers to a preferred embodiment of the applicants fluidic function generator. Function generator 10 comprises input means 11, a fluidic variable gain circuit 12, a control circuit 13 and output means 14.

Input means 11 comprises a proportional amplifier 15 having a power nozzle 16, a first pair of control ports 17 and 18, a second pair of control ports 19 and 20 and a pair of outlet passages 21 and 22. Power nozzle 16 is continuously supplied with fluid under pressure by means of conduit 23 from a fluid source 24 which is common to many elements in this circuit. Fluid source 24 also supplies variable bias pressures to control ports 19 and 20 by means of conduits 23, 25 and 26, valves 27 and 28 and conduits 29 and 30. Fluid source 24, conduits 23, 25 and 26, valves 27 and 28 and conduits 29 and 30 cooperate to form a variable bias means 31. It should be noted that this bias means configuration is shown for purposes of illustration only. Many other bias means configurations may also be utilized. The bias pressure may, for example. be supplied by circuits external to function generator Ill,

Variable gain circuit 12 may be of any suitable type wherein gain changes are accomplished by means of a fluid gain control signal supplied thereto. The particular variable gain circuit illustrated in FIG. 1 is the circuit disclosed in the copending application of Charles W. Rainer, Ser. No. 659,964, filed August 11, 1967, now U. S. Pat. No. 3,499,490 and assigned to the assignee of the present application.

Variable gain circuit 12 comprises a first proportional fluid amplifier 35, a second proportional fluid amplifier 36 and a third proportional fluid amplifier 37. Amplifier includes a power nozzle 38, a first pair of control ports 39 and 40, a second pair of control ports 41 and 42 and a pair of outlet passages 43 and 44. Power nozzle 38 is continuously supplied with fluid under pressure from fluid source 24 by means of a conduit 45.

Amplifiers 36 and 37 are substantially identical in geometry. Amplifier 36 includes a power nozzle 50, a pair of control ports 5] and 52 and a pair of outlet passages 53 and 54. Amplifier 37 includes a power nozzle 55, a pair of control ports 56 and 57 and a pair ofoutlet passages 58 and 59.

Outlet passages 43 and 44 of amplifier 35 are connected to power nozzles and of amplifiers 36 and 37 by means of conduits 60 and 6]. Outlet passages 53 and 59 of amplifiers 36 and 37 are connected to control ports 41 and 42 of amplifier 35 by means of conduits 62 and 63. Control ports 51 and 57 of amplifiers 36 and 37 are supplied with a common variable bias pressure by means of fluid source 24, a conduit 65, a valve 66, and conduits 67, 68 and 69. Other suitable means for supplying a bias pressure to control ports 51 and 57 will also be apparent to those skilled in the fluidics art. Control ports 52 and 56 of amplifiers 36 and 37 are supplied with a common gain control signal from control circuit 13 as will hereinafter be discussed.

Control ports 39 and 40 of amplifier constitute the inlet to variable gain circuit 12. Control ports 39 and 40 are con nected to outlet passages 21 and 22 of amplifier 15, which constitute the outlet of input means 11, by means of conduits and 71.

Control circuit 13 is shown as comprising a cascade ofthree fluid amplifiers 75, 76 and 77. Amplifier includes a power nozzle 80, a pair of control ports 81 and 82 and a pair of outlet passages 83 and 84. Power nozzle is continuously supplied with fluid under pressure from fluid source 24 by means ofa conduit 85.

Amplifier 76 includes a power nozzle 90, a first pair of control ports 91 and 92, a second pair of control ports 93 and 94 and a pair of outlet passages 95 and 96. Power nozzle 90 is continuously supplied with fluid under pressure from fluid source 24 by means of conduit 97. Control ports 91 and 92 are connected to outlet passages 83 and 84 of amplifier 75 by means of conduits and 101. Control ports 93 and 94 are supplied with variable bias pressures by means of variable bias means 102. Variable bias means 102 is similar to variable bias means 31 and need not be described in further detail.

Amplifier 77 includes a power nozzle 110, a pair of control ports 111 and 112 and a pair of outlet passages 113 and 114. Power nozzle is supplied with fluid under variable pressure from fluid source 24 by means of conduit 115, valve 116 and conduit 117. Fluid source 24, conduit 115 and valve 116 comprise a variable power supply. It should be noted that power nozzle 110 can be supplied with fluid under variable pressure by means other than those illustrated. For example, power nozzle 110 can be supplied by means ofa fluidic circuit external to function generator 10. Control ports 111 and 112 are connected to outlet passages 95 and 96 of amplifier 76 by means ofconduits 120 and 121.

Control ports 81 and 82 of amplifier 75 constitute the inlet to control circuit 13. Control ports 81 and 82 are connected to outlet passages 21 and 22 ofamplifier 15 by means of conduits 70, 71, and 131. outlet passage 114 of amplifier 77 constitutes the outlet of control circuit 13. Outlet passage 114 is connected to control ports 52 and 56 of amplifiers 36 and 37 by means of conduits 132 and 133.

Amplifiers 75 and 76 of control circuit 13 are proportional devices. Amplifier 77 may be either a proportional or a bistable device depending upon the function desired from function generator 10. Other suitable control circuit configurations may contain more or fewer amplifiers. Further, in some cases it may be unnecessary to provide variable supply and bias pressures to control circuit 13. The functions desired from function generator 10 determine the most suitable configuration for control circuit 13.

Output means 14 comprises a proportional fluid amplifier 135 having a power nozzle 136, a first pair of control ports 137 and 138, a second pair of control ports 139 and 140 and a pair of outlet passages 141 and 142. Power nozzle 136 is continuously supplied with fluid under pressure from fluid source 24 by means of a conduit 143. Control ports 137 and 138 are connected to outlet passages 54 and 58 of amplifiers 36 and 37, which constitute the outlet of variable gain circuit 12, by means of conduits 145 and 146. Control ports 139 and 140 are supplied with variable bias pressures by means of variable bias means 147. Variable bias means 147 is similar to variable bias means 31 and need not be described in further detail.

' Control ports 17 and 18 ofamplifier 15 constitute the signal inlet to function generator 10. 'Control ports 17 and 18 may be connected to any suitable source of pressure differential input signals (not shown) by means of conduits 150 and 151. Similarly, outlet passages 141 and 142 of amplifier 135 constitute the signal outlet of function generator 10. ,Outlet passages 141 and 142 may be connected to any suitable utilization device (not shown) by means of conduits 152 and 153. v In order to gain a proper understanding of the applicants unique function generator, it is first necessary to understand the operation of variable gain circuit 12. Referring now to the operation of circuit 12, fluid from fluid source 24 issues as a stream from power nozzle 38. In the absence of a pressure differential between control ports 39 and 40, the fluid stream from power nozzle 38 will divide substantially equally between outlet passages 43 and 44. This results in fluid being supplied to power nozzles 50 and 55 of amplifiers 36 and 37 at substantially equal pressures.

Amplifiers 36 and 37 have substantially identical geometries. Control ports 51 and 57 are connected to the same bias pressure source and are therefore supplied with equal pressures and control ports 52 and 56 are connected to the same gain control signal source and are therefore supplied with equal pressures. Consequently, fluid will flow from outlet passages 54 and 58 at substantially equal pressures. Accordingly, in the absence of a pressure differential input signal, there will be no pressure differential output signal from circuit 12.

If, however, an input signal is applied to circuit 12 such that the pressure is greater at control port 40 than at control port 39, the fluid stream issuing from power nozzle 38 will be deflected such that a larger portion thereof enters outlet passage 43. As a result, fluid is supplied to amplifier 36 at a 'higher pressure than to amplifier 37. Amplifiers 36 and 37 have substantially equal geometries. The same bias pressure is supplied to control ports 51 and 57 and the same gain control signal is provided to control ports 52 and 56. Therefore, the stream issuing from power nozzle 50 will divide between outlet passages 53 and 54 in substantially the same proportion as the stream issuing from power nozzle 55 divides between outlet passages 58 and 59. However, since fluid is issuing from power nozzle 50 at a higher pressure than from power nozzle 55, fluid will flow from outlet passage 54 at a higher pressure than from outlet passage 58. Thus, if a pressure differential input signal is applied to circuit 12, a pressure differential out put signal will be provided therefrom.

If a pressure differential exists between outlet passages 54 and 58, a pressure differential will also exist between outlet passages 53 and 59. The pressure differential between outlet passages 53 and 59 constitutes a negative feedback signal which is transmitted to control ports 41 and 42 of amplifier 35 by means of conduits 62 and 63. This negative feedback signal tends to counteract any pressure differential signal supplied to control ports 39 and 40. However, the negative feedback portions of circuit 12, including control ports 41 and 42, are designed to be less effective at controlling the stream issuing from power nozzle 38 than control ports 39 and 40. Consequently, the negative feedback does not overcome the effect of the pressure differential at control ports 39 and 40, but serves to increase the linear operating range and stability of circuit 12.

Considering any given input signal to circuit 12, maximum pressure signal in outlet passage 54 will occur when the stream issuing from power nozzle 50 is deflected directly into outlet passage 54. Likewise, a maximum pressure signal in outlet passage 58 will occur when the stream issuing from power nozzle 55 is deflected directly into outlet passage 58. The streams issuing from power nozzles 50 and 55 can be directed toward outlet passages 54 and 58 respectively by supplying a bias pressure to control ports 51 and 57 which is sufficiently greater than the gain control pressure supplied to control ports 52 and 56.'This bias condition results in a maximum pressure differential between outlet passages 54 and 58 and also results in a maximum circuit gain.

increasing the gain control pressure at control ports 52 and 56 from the value required for maximum circuit gain causes the streams from power nozzles 50 and 55 to be deflected away from outlet passages 54 and 58. The result is that the pressures of the fluid signals in both outlet passages 54 and 58 decrease. Consequently, the circuit gain decreases. The circuit gain can be reduced to zero by sufficiently increasing the gain control pressure at control ports 52 and 56 relative to the bias pressure at control ports 51 and 57.

Amplifier 15 of input means 11 and amplifier 135 of output means 14 are proportional devices and are of such a size and design that they normally operate in their linear operating ranges. Therefore, assuming that a constant gain control pressure is maintained at control ports 52 and 56 of amplifiers 36 and 37, a plot of the output signal of function generator versus time willhave the same general shape as a plot of the input signal versus time. However, the magnitude of the output signals will be altered by the composite gain of input means 11, variable gain circuit 12 and output means 14. The composite gain of the input means 11, variable gain circuit 12 and output means 14 will be maximized when the gain of variable gain circuit 12 has its maximum value. Similarly, the composite gain has a zero value when the gain of variable gain circuit 12 is zero.

If the output of amplifier 77 is held constant, thus providing a constant gain control pressure, the gain of function generator 10 will be given by one of a plurality of continuous substantially linear mathematical functions. These functions can be represented by curves having slopes from zero to some maximum value corresponding to the maximum gain of function generator 10. However, the output of amplifier 77 will not, in general, remain constant. Assume, for example, that the input signal to function generator 10 is changing such that the pressure supplied to control port 17 of amplifier 15 is increasing relative to the pressure supplied to control port 18. Further, assume that the pressure at control port 17 is initially much lower than the pressure at control port 18. Thus, the pressure in outlet passage 22 of amplifier 15 is initially much less than the pressure in outlet passage 21. However, the pressure in outlet passage 22 is increasing relative to the pressure in outlet passage 21. This signal is transmitted to control ports 81 and 82 of amplifier 75 in control circuit 13. Accordingly, the pressure in outlet passage 83 of amplifier 75 is initially much lower than the pressure in outlet passage 84. However, the pressure in outlet passage 83 is increasing relative to the pressure in outlet passage 84.

The pressure signals from amplifier 75 are transmitted to control ports 91 and 92 of amplifier 76, The output signals from amplifier 76 are dependent on both the input signals supplied thereto and the setting of the valves in variable bias means 102. Thus, the effect of a pressure at control port 92, which is initially much greater than the pressure at control port 91, may be counteracted by the effect of a bias pressure at control port 93 which is much greater than the bias pressure at control port 94. However, if the pressure at control port 91 is increasing relative to that at control port 92, the pressure in outlet passage 96 will increase relative to the pressure in outlet passage 95 regardless of whether or not the pressure signals from outlet passages 95 and 96 are offset due to the bias pressures supplied by variable bias means 102. The purpose served by variable bias means 102 will hereinafter be further discussed.

The pressure signals from amplifier 76 are supplied to control ports 111 and 112 of amplifier 77. If amplifier 77 is bistable, its output will be switched from outlet passage 113 to outlet passage 114 when the pressure at control port 111 becomes greater than the pressure at control port 112 by an amount sufficient to cause amplifier 77 to switch. If amplifier 77 is proportional, its output will be gradually transferred from outlet passage 113 to outlet passage 114 as the pressure at control port 111 increases from a value less than that at control port 112 to a value greater than that at control port 112.

The maximum pressures which can be provided in outlet passages 113 and 114 are determined by the pressure supplied to power nozzle 110. The pressure supplied to power nozzle 110 is controlled by the setting of valve 116. The purpose served by valve 116, which is a part ofa variable power supply comprising fluid source 24, conduit 115 and valve 116, will hereinafter be further discussed.

The operation of function generator 10 will first be discussed on the basis that amplifier 77 is bistable. In FIG. 2,

combinations of any one of curves A0, B0, C0 and E0 with any one of curves OF, OH, OJ and OK represent typical gain relationships for this embodiment of function generator 10. The input signal, designated AP input, is a pressure differential applied between control ports 17 and 18 of amplifier 15 and is represented by a distance from the ordinate axis in FIG. 2. The output signal, designated AP output, is a pressure differential produced between outlet passages 141 and 142 of amplifier and is represented by a distance from the abscissa axis. The maximum gain of function generator 10 results when the gain control pressure is zero and the bias pressure supplied to control ports 51 and 57 of amplifiers 36 and 37 is such that the fluid streams issuing from power nozzles 50 and 55 are directed toward outlet passages 54 and 58. This gain can be represented by the curve EOF. The minimum gain of function generator 10'results when the gain control pressure is of sufficient magnitude to direct substantially the entire power streams of amplifiers 36 and 37 away from outlet passages 54 and 58 and toward outlet passages 53 and 59. This gain can be represented by a line coinciding with the abscissa axis. Further, the gain of function generator 10 may assume any intermediate value, such as can be represented by curves AOK, B0] and COH by providing a gain control pressure at control ports 52 and 56 of amplifiers 36 and 37 which has the proper value relative to the bias pressure at control ports 51 and 57.

The functions represented by curves AOK, BOJ, COH and EOF are all continuous substantially linear functions. However, function generator 10 can also generate discontinuous functions. For example, a typical application for function generator 10 is in a fuel control system for a turbojet engine. The mathematical function required for such an application may be the function represented by curve BOF in FIG. 2 wherein AP'input is a signal indicative ofthe speed ofthe compressor and/or turbine within a turbojet engine and AP output is a signal indicative of the rate at which fuel can be used by the engine. AP input is produced by means external to function generator 10 and is transmitted to control ports 17 and 18 of amplifier 15 by means of conduits and 151. AP output is transmitted from outlet passages 141 and 142 of amplifier 135 to fuel control means (not shown) by means of conduits 152 and 153.

In the operation of this fuel control system, assume that the pressures transmitted to control ports 17 and 18 are equal when the compressor is stationary. Further, assume that the pressure transmitted to control port 17 increases with respect to that transmitted to control port 18 as the compressor speed increases, As a result, the pressure produced in outlet passage 142 of amplifier 135 increases with respect to the pressure produced in outlet passage 141 as the compressor speed increases. However, as shown by curve BOF, the rate at which fuel can be used by the engine increases at a more rapid rate for compressor speeds greater than a given speed than it does for compressor speeds less than the given speed. For purposes of the following discussion, 3000 RPM will be taken as atypical speed for this transition to occur. In order to achieve the input signal versus output relationship represented by curve BOF, the gain of function generator 10 must be greater for compressor speeds above 3000 RPM than it is for compressor speeds below'3000 RPM. Thus, as the compressor speed increases from standstill to its maximum speed, the gain of function generator 10 must increase when the compressor reaches 3000 RPM. Control circuit 13 operates to automatically change the gain of function generator 10 in the required manner as will hereinafter be discussed.

Since amplifier 77 is bistable, substantially all of its output will be from either outlet passage 113 or outlet passage 114. Thus, the pressure in outlet passage 114, which is the gain control pressure. can assume either one oftwo values. These values are essentially zero and some positive value dependent on the pressure of fluid source 24 and the setting of valve 116. From the previous discussion, item be seen that variable gain circuit 12, and consequently function generator 10, will have maximum gains for a given bias pressure at control ports 51 and 57 ifthe gain control pressure at control ports 52 and 56 is zero. Portion OF of curve BOF represents the maximum gain required from function generator in producing the desired function. A function which can be represented by a curve having the same slope as curve OF is generated by adjusting valve 66 such that the bias pressure supplied to control ports 51 and 57 causes function generator 10 to have the required gain when the gain control pressure is zero. The gain control pressure can be made substantially zero by causing the output signal of amplifier 77 to be from outlet passage 113. The maximum gain of function generator 10 and the maximum slope of the curve representing the generated function are thus controlled by the bias pressure supplied to control ports 51 and 57.

Portion B0 of curve BOF represents a lower gain than that represented by portion OF. A function which can be represented by a curve having the same slope as BO can be generated, without changing the setting of valve 66, by giving the gain control pressure a particular positive value. The gain control pressure can be given this value by causing the output signal of amplifier 77 to be from outlet passage 114 and adjusting valve 116 such that the required gain control pressure is produced.

It can be seen that the output of amplifier 77 must be switched in proper relationship to the input signal to amplifier in order to generate the function represented by curve BOF. Thus, the switching signal for amplifier 77 is derived from the input signal as follows. As the compressor speed increases, the pressure in outlet passage 22 of amplifier 15 increases with respect to that in outlet passage 21. The pressure signals from amplifier 15 are transmitted to control circuit 13 through control ports 81 and 82 of amplifier 75, thereby causing the pressure in outlet passage 83 to increase with respect to that in outlet passage 84. The pressure signals from amplifier 75 are supplied to control ports 91 and 92 of amplifier 76, thereby causing the pressure in outlet passage 96 to increase with respect to that in outlet passage 95. The output signals from amplifier 76 are, in turn, supplied to control ports 111 and 112 of amplifier 77. Accordingly, as the compressor speed increases, the pressure supplied to control port 112 will become increasingly larger than that supplied to control port 111, thereby causing the output from amplifier 77 to be switched from outlet passage 114 to outlet passage 113. Func tion generator 10 is thus switched from a gain represented by curve B0] to a gain represented by curve EOF.

It has been shown how function generator 10 is switched from one gain to another. However, it will be recognized that the magnitude of the output signal from function generator 10 may not have the same value for both gains at the time the gain is changed. If the output signal does not have identical magnitudes for both gains, a step will be created in the curve representing the generated function at the point of discontinuity. However, function generator 10 can be caused to switch at a time when its output signal has identical magnitudesfor both gains by adjusting the valves in variablebias means 102 such that appropriate bias pressures are supplied to control ports 93 and 94 of amplifier 76. Amplifier 76 functions to sum the incoming signals and the bias pressures supplied thereto such that amplifier 77 is switched at a time when the output of amplifier 135 has the samevalue with either gain of variable gain circuit 12. Thus, the two portions of the curve representing the generated function can be made to have a common value at the point of discontinuity as is illustrated by curve BOF.

As previously noted, bias pressures from variable bias means 31 are supplied to amplifier 15. Amplifier l5 sums these bias pressures with the input signals, thus offsetting the effect of the input signals. Further, the bias pressures from variable bias means 31 have the effect'of shifting the curve representing the generated function to the left or right along the abscissa axis in FIG. 2. Similarly, the bias pressures from variable bias means 147, which are supplied to amplifier 135, have the effect of offsetting the output signals. Accordingly,

the curve representing the generated function can be shifted up or down along the ordinate axis.

More specifically, if valves 27 and 28 of variable bias means 31 are set such that the bias pressure at control port 19 is greater than the bias pressure at control port 20, the entire curve representing the generated function will be shifted to the left along the abscissa axis. Conversely, if the valves of variable bias means 3] are set such that bias pressure at control port 20 is greater than the bias pressure at control port 19, the entire curve will shift to the right along the abscissa axis. Similarly, if the valves in variable bias means 147 are set such that the bias pressure at control port 139 is greater than the bias pressure at control port 140, the entire curve will be shifted up along the ordinate axis. 1f the valves in variable bias means 147 are set such that the bias pressure at control port 140 is greater than the bias pressure at control port 139, the entire curve will be shifted down along the ordinate axis. The effects of variable bias means 31 and 147 are independent. Therefore, the entire gain curve may be shifted in any direction with respect to the origin of the coordinate axis system.

Accordingly, the curve BOF can be shifted to the right along the abscissa axis such that point 0 coincides with the input pressure differential corresponding to a compressor speed of 3000 RPM. Similarly, if the fuel control means only operates on positive pressure differential signals, curve BOF can be shifted upward until the entire curve lies above the ordinate axis, thus representing an output pressure differential which is always positive.

Other discontinuous functions may be required for other applications. From the foregoing discussion it can be seen the functions represented by various combinations of portions of the curves illustrated in FIG. 2 can be generated by appropriately adjusting valves 66 and 116. lt is pointed out that the previously discussed functions are all represented by curves, the right hand portion of which, as viewed in FIG. 2, has an equal or greater slope than the left hand portion. Function generator 10 is also capable of generating functions which can be represented by curves in which the left hand portion has an equal or greater slope than the right hand portion. This may be accomplished by taking the gain control pressure for variable gain circuit 10 from outlet passage 113 of amplifier 77 rather than from outlet passage 114.

it can be seen that if amplifier 77 is a bistable device, the gain control pressure supplied to control ports 52 and 56 changes instantaneously when the input signal to generator 10 reaches a predetermined pressure. The curve representing the gain of function generator 10 is therefore discontinuous as shown at O in FIG. 2. However, if amplifier 77 is a proportional device, its output will gradually be transferred from one outlet passage to the other as the magnitude of the input signal changes. Thus, the gain of variable gain circuit will change continuously as the magnitude of the input signal changes. The function generated by function generator 10 will then be a continuous nonlinear function which can be represented by a smooth curve having a gradually changing slope such as curve DOG in FIG. 2.

The maximum and minimum gains of this embodiment can be controlled by valves 66 and 116 in the same manner describedfor the embodiment wherein amplifier 77 is bistable. Further, the entire curve representing the generated function can be shifted in any direction with respect to a fixed set of coordinate axes by appropriately adjusting bias means 13 and 147 in the manner previously described for the embodiment wherein amplifier 77 is bistable.

In accordance with the previous description, the applicants invention overcomes disadvantages of the prior art fluidic function generators by allowing changing of the generated function without the necessity of structurally altering the generator. Further, the applicant has provided an unique function generating circuit which is easily adaptable to a wide variety of applications.

Although the applicant's invention has been described and illustrated in detail, it should be understood that the same is by way of illustration and example only and is not to be taken by way of limitation. The spirit and scope of this invention are limited only by the terms ofthe following claims.

l claim:

1. A fluidic function generator comprising:

input means including an inlet and an outlet;

a variable gain circuit including an inlet, an outlet and a gain control port;

means connecting the outlet of said input means to the inlet of said variable gain circuit;

gain control means including an inlet and an outlet;

means connecting the outlet of said input means to the inlet of said gain control means; and

means connecting the outlet of said gain control means to the gain control port of said variable gain circuit.

2. The fluidic function generator of claim 1 wherein said gain control means includes a fluid amplifier.

3. The fluidic function generator of claim 1 further including:

first variable bias means;

means connecting said first variable bias means to said input means;

output means including an inlet and an outlet;

means connecting the outlet of said variable gain circuit to the inlet of said output means;

second variable bias means; and

means connecting said second variable bias means to said output means.

4. The fluidic function generator of claim I wherein said gain control means comprises:

a cascade of proportional fluid amplifiers;

first variable bias means; and

means connecting said first variable bias means to an amplifier in said cascade of amplifiers.

5. The fluidic function generator of claim 4 wherein said gain control means further includes variable power supply means and means connecting said variable power supply means to an amplifier in said gain control means.

6. The fluidic function generator of claim 5 further including:

second variable bias means;

means connecting said second variable bias means to said input means;

output means including an inlet and an outlet;

means connecting the outlet of said variable gain circuit to the inlet of said output means;

third variable bias means; and

means connecting said third variable bias means to said output means.

7. The fluidic function generator of claim 1 wherein:

said variable gain circuit further includes a bias port, a first variable bias means and means connecting said first variable bias means to said bias port; and

said gain control means comprises a cascade of fluid amplifiers including a bistable fluid amplifier, second variable bias means, means connecting said second variable bias means to an amplifier in said cascade of amplifiers, variable power supply means, and means connecting said variable power supply means to said bistable fluid amplifier.

8. The fluidic function generator of claim 7 further including:

third variable bias means;

means connecting said third variable bias means to said input means;

output means including an inlet and an outlet;

means connecting the outlet of said variable gain circuit to the inlet of said output means;

fourth variable bias means; and

means connecting said fourth variable bias means to said output means.

9. In combination:

variable gain apparatus including an inlet, an outlet and a gain control port;

input means; and

connecting means including fluid amplifier means for connecting said input means to the inlet and the gain control port of said variable gain apparatus.

10. The combination according to claim 9 wherein said connecting means comprises:

a cascade offluid amplifiers including a bistable fluid amplifier;

first variable bias means;

means connecting said first variable bias means to an amplifier in said cascade of amplifiers;

variable power supply means; and

means connecting said variable power supply means to said bistable fluid amplifier.

ll. The combination according to claim 9 further including:

first variable bias means;

means connecting said first variable bias means to said input means: output means including an inlet and an outlet:

means connecting the outlet of said variable gain circuit to the inlet of said output means;

second variable bias means; and

means connecting said second variable bias means to said output means. 

